I have a 2004 TDI 5 speed Automatic 2.0 L. When I turn the cabin heater fan on it will run initially just fine but after few seconds it starts to slow and after about 5 seconds it appears not to be blowing any air at all. Does anyone know what might be causing this?
Thanks,

Dry bearings that bind as the blower motor warms up. Clean and lube it and see if that helps.

- Tim

And probably continuing to use it in this condition will burn out the resistor pack thermal fuse, or the blower power supply fuse.
Try the lube the bearings route or replace the blower/motor. It's pretty easy deal.